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This is Info file ../../info/lispref.info, produced by Makeinfo version 1.68 from the input file lispref.texi. Edition History: GNU Emacs Lisp Reference Manual Second Edition (v2.01), May 1993 GNU Emacs Lisp Reference Manual Further Revised (v2.02), August 1993 Lucid Emacs Lisp Reference Manual (for 19.10) First Edition, March 1994 XEmacs Lisp Programmer's Manual (for 19.12) Second Edition, April 1995 GNU Emacs Lisp Reference Manual v2.4, June 1995 XEmacs Lisp Programmer's Manual (for 19.13) Third Edition, July 1995 XEmacs Lisp Reference Manual (for 19.14 and 20.0) v3.1, March 1996 XEmacs Lisp Reference Manual (for 19.15 and 20.1, 20.2) v3.2, April, May 1997 Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995 Free Software Foundation, Inc. Copyright (C) 1994, 1995 Sun Microsystems, Inc. Copyright (C) 1995, 1996 Ben Wing. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the section entitled "GNU General Public License" is included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the section entitled "GNU General Public License" may be included in a translation approved by the Free Software Foundation instead of in the original English. File: lispref.info, Node: Character Type, Next: Symbol Type, Prev: Floating Point Type, Up: Programming Types Character Type -------------- In XEmacs version 19, and in all versions of FSF GNU Emacs, a "character" in XEmacs Lisp is nothing more than an integer. This is yet another holdover from XEmacs Lisp's derivation from vintage-1980 Lisps; modern versions of Lisp consider this equivalence a bad idea, and have separate character types. In XEmacs version 20, the modern convention is followed, and characters are their own primitive types. (This change was necessary in order for MULE, i.e. Asian-language, support to be correctly implemented.) Even in XEmacs version 20, remnants of the equivalence between characters and integers still exist; this is termed the "char-int confoundance disease". In particular, many functions such as `eq', `equal', and `memq' have equivalent functions (`old-eq', `old-equal', `old-memq', etc.) that pretend like characters are integers are the same. Byte code compiled under any version 19 Emacs will have all such functions mapped to their `old-' equivalents when the byte code is read into XEmacs 20. This is to preserve compatibility - Emacs 19 converts all constant characters to the equivalent integer during byte-compilation, and thus there is no other way to preserve byte-code compatibility even if the code has specifically been written with the distinction between characters and integers in mind. Every character has an equivalent integer, called the "character code". For example, the character `A' is represented as the integer 65, following the standard ASCII representation of characters. If XEmacs was not compiled with MULE support, the range of this integer will always be 0 to 255 - eight bits, or one byte. (Integers outside this range are accepted but silently truncated; however, you should most decidedly *not* rely on this, because it will not work under XEmacs with MULE support.) When MULE support is present, the range of character codes is much larger. (Currently, 19 bits are used.) FSF GNU Emacs uses kludgy character codes above 255 to represent keyboard input of ASCII characters in combination with certain modifiers. XEmacs does not use this (a more general mechanism is used that does not distinguish between ASCII keys and other keys), so you will never find character codes above 255 in a non-MULE XEmacs. Individual characters are not often used in programs. It is far more common to work with *strings*, which are sequences composed of characters. *Note String Type::. The read syntax for characters begins with a question mark, followed by the character (if it's printable) or some symbolic representation of it. In XEmacs 20, where characters are their own type, this is also the print representation. In XEmacs 19, however, where characters are really integers, the printed representation of a character is a decimal number. This is also a possible read syntax for a character, but writing characters that way in Lisp programs is a very bad idea. You should *always* use the special read syntax formats that XEmacs Lisp provides for characters. The usual read syntax for alphanumeric characters is a question mark followed by the character; thus, `?A' for the character `A', `?B' for the character `B', and `?a' for the character `a'. For example: ;; Under XEmacs 20: ?Q => ?Q ?q => ?q (char-int ?Q) => 81 ;; Under XEmacs 19: ?Q => 81 ?q => 113 You can use the same syntax for punctuation characters, but it is often a good idea to add a `\' so that the Emacs commands for editing Lisp code don't get confused. For example, `?\ ' is the way to write the space character. If the character is `\', you *must* use a second `\' to quote it: `?\\'. XEmacs 20 always prints punctuation characters with a `\' in front of them, to avoid confusion. You can express the characters Control-g, backspace, tab, newline, vertical tab, formfeed, return, and escape as `?\a', `?\b', `?\t', `?\n', `?\v', `?\f', `?\r', `?\e', respectively. Their character codes are 7, 8, 9, 10, 11, 12, 13, and 27 in decimal. Thus, ;; Under XEmacs 20: ?\a => ?\^G ; `C-g' (char-int ?\a) => 7 ?\b => ?\^H ; backspace, <BS>, `C-h' (char-int ?\b) => 8 ?\t => ?\t ; tab, <TAB>, `C-i' (char-int ?\t) => 9 ?\n => ?\n ; newline, <LFD>, `C-j' ?\v => ?\^K ; vertical tab, `C-k' ?\f => ?\^L ; formfeed character, `C-l' ?\r => ?\r ; carriage return, <RET>, `C-m' ?\e => ?\^[ ; escape character, <ESC>, `C-[' ?\\ => ?\\ ; backslash character, `\' ;; Under XEmacs 19: ?\a => 7 ; `C-g' ?\b => 8 ; backspace, <BS>, `C-h' ?\t => 9 ; tab, <TAB>, `C-i' ?\n => 10 ; newline, <LFD>, `C-j' ?\v => 11 ; vertical tab, `C-k' ?\f => 12 ; formfeed character, `C-l' ?\r => 13 ; carriage return, <RET>, `C-m' ?\e => 27 ; escape character, <ESC>, `C-[' ?\\ => 92 ; backslash character, `\' These sequences which start with backslash are also known as "escape sequences", because backslash plays the role of an escape character; this usage has nothing to do with the character <ESC>. Control characters may be represented using yet another read syntax. This consists of a question mark followed by a backslash, caret, and the corresponding non-control character, in either upper or lower case. For example, both `?\^I' and `?\^i' are valid read syntax for the character `C-i', the character whose value is 9. Instead of the `^', you can use `C-'; thus, `?\C-i' is equivalent to `?\^I' and to `?\^i': ;; Under XEmacs 20: ?\^I => ?\t ?\C-I => ?\t (char-int ?\^I) => 9 ;; Under XEmacs 19: ?\^I => 9 ?\C-I => 9 There is also a character read syntax beginning with `\M-'. This sets the high bit of the character code (same as adding 128 to the character code). For example, `?\M-A' stands for the character with character code 193, or 128 plus 65. You should *not* use this syntax in your programs. It is a holdover of yet another confoundance disease from earlier Emacsen. (This was used to represent keyboard input with the <META> key set, thus the `M'; however, it conflicts with the legitimate ISO-8859-1 interpretation of the character code. For example, character code 193 is a lowercase `a' with an acute accent, in ISO-8859-1.) Finally, the most general read syntax consists of a question mark followed by a backslash and the character code in octal (up to three octal digits); thus, `?\101' for the character `A', `?\001' for the character `C-a', and `?\002' for the character `C-b'. Although this syntax can represent any ASCII character, it is preferred only when the precise octal value is more important than the ASCII representation. ;; Under XEmacs 20: ?\012 => ?\n ?\n => ?\n ?\C-j => ?\n ?\101 => ?A ?A => ?A ;; Under XEmacs 19: ?\012 => 10 ?\n => 10 ?\C-j => 10 ?\101 => 65 ?A => 65 A backslash is allowed, and harmless, preceding any character without a special escape meaning; thus, `?\+' is equivalent to `?+'. There is no reason to add a backslash before most characters. However, you should add a backslash before any of the characters `()\|;'`"#.,' to avoid confusing the Emacs commands for editing Lisp code. Also add a backslash before whitespace characters such as space, tab, newline and formfeed. However, it is cleaner to use one of the easily readable escape sequences, such as `\t', instead of an actual whitespace character such as a tab. File: lispref.info, Node: Symbol Type, Next: Sequence Type, Prev: Character Type, Up: Programming Types Symbol Type ----------- A "symbol" in XEmacs Lisp is an object with a name. The symbol name serves as the printed representation of the symbol. In ordinary use, the name is unique--no two symbols have the same name. A symbol can serve as a variable, as a function name, or to hold a property list. Or it may serve only to be distinct from all other Lisp objects, so that its presence in a data structure may be recognized reliably. In a given context, usually only one of these uses is intended. But you can use one symbol in all of these ways, independently. A symbol name can contain any characters whatever. Most symbol names are written with letters, digits, and the punctuation characters `-+=*/'. Such names require no special punctuation; the characters of the name suffice as long as the name does not look like a number. (If it does, write a `\' at the beginning of the name to force interpretation as a symbol.) The characters `_~!@$%^&:<>{}' are less often used but also require no special punctuation. Any other characters may be included in a symbol's name by escaping them with a backslash. In contrast to its use in strings, however, a backslash in the name of a symbol simply quotes the single character that follows the backslash. For example, in a string, `\t' represents a tab character; in the name of a symbol, however, `\t' merely quotes the letter `t'. To have a symbol with a tab character in its name, you must actually use a tab (preceded with a backslash). But it's rare to do such a thing. Common Lisp note: In Common Lisp, lower case letters are always "folded" to upper case, unless they are explicitly escaped. In Emacs Lisp, upper case and lower case letters are distinct. Here are several examples of symbol names. Note that the `+' in the fifth example is escaped to prevent it from being read as a number. This is not necessary in the sixth example because the rest of the name makes it invalid as a number. foo ; A symbol named `foo'. FOO ; A symbol named `FOO', different from `foo'. char-to-string ; A symbol named `char-to-string'. 1+ ; A symbol named `1+' ; (not `+1', which is an integer). \+1 ; A symbol named `+1' ; (not a very readable name). $*\ 1\ 2$ ; A symbol named `(* 1 2)' (a worse name). +-*/_~!@$%^&=:<>{} ; A symbol named `+-*/_~!@$%^&=:<>{}'. ; These characters need not be escaped. File: lispref.info, Node: Sequence Type, Next: Cons Cell Type, Prev: Symbol Type, Up: Programming Types Sequence Types -------------- A "sequence" is a Lisp object that represents an ordered set of elements. There are two kinds of sequence in XEmacs Lisp, lists and arrays. Thus, an object of type list or of type array is also considered a sequence. Arrays are further subdivided into strings, vectors, and bit vectors. Vectors can hold elements of any type, but string elements must be characters, and bit vector elements must be either 0 or 1. However, the characters in a string can have extents (*note Extents::.) and text properties (*note Text Properties::.) like characters in a buffer; vectors do not support extents or text properties even when their elements happen to be characters. Lists, strings, vectors, and bit vectors are different, but they have important similarities. For example, all have a length L, and all have elements which can be indexed from zero to L minus one. Also, several functions, called sequence functions, accept any kind of sequence. For example, the function `elt' can be used to extract an element of a sequence, given its index. *Note Sequences Arrays Vectors::. It is impossible to read the same sequence twice, since sequences are always created anew upon reading. If you read the read syntax for a sequence twice, you get two sequences with equal contents. There is one exception: the empty list `()' always stands for the same object, `nil'. File: lispref.info, Node: Cons Cell Type, Next: Array Type, Prev: Sequence Type, Up: Programming Types Cons Cell and List Types ------------------------ A "cons cell" is an object comprising two pointers named the CAR and the CDR. Each of them can point to any Lisp object. A "list" is a series of cons cells, linked together so that the CDR of each cons cell points either to another cons cell or to the empty list. *Note Lists::, for functions that work on lists. Because most cons cells are used as part of lists, the phrase "list structure" has come to refer to any structure made out of cons cells. The names CAR and CDR have only historical meaning now. The original Lisp implementation ran on an IBM 704 computer which divided words into two parts, called the "address" part and the "decrement"; CAR was an instruction to extract the contents of the address part of a register, and CDR an instruction to extract the contents of the decrement. By contrast, "cons cells" are named for the function `cons' that creates them, which in turn is named for its purpose, the construction of cells. Because cons cells are so central to Lisp, we also have a word for "an object which is not a cons cell". These objects are called "atoms". The read syntax and printed representation for lists are identical, and consist of a left parenthesis, an arbitrary number of elements, and a right parenthesis. Upon reading, each object inside the parentheses becomes an element of the list. That is, a cons cell is made for each element. The CAR of the cons cell points to the element, and its CDR points to the next cons cell of the list, which holds the next element in the list. The CDR of the last cons cell is set to point to `nil'. A list can be illustrated by a diagram in which the cons cells are shown as pairs of boxes. (The Lisp reader cannot read such an illustration; unlike the textual notation, which can be understood by both humans and computers, the box illustrations can be understood only by humans.) The following represents the three-element list `(rose violet buttercup)': ___ ___ ___ ___ ___ ___ |___|___|--> |___|___|--> |___|___|--> nil | | | | | | --> rose --> violet --> buttercup In this diagram, each box represents a slot that can refer to any Lisp object. Each pair of boxes represents a cons cell. Each arrow is a reference to a Lisp object, either an atom or another cons cell. In this example, the first box, the CAR of the first cons cell, refers to or "contains" `rose' (a symbol). The second box, the CDR of the first cons cell, refers to the next pair of boxes, the second cons cell. The CAR of the second cons cell refers to `violet' and the CDR refers to the third cons cell. The CDR of the third (and last) cons cell refers to `nil'. Here is another diagram of the same list, `(rose violet buttercup)', sketched in a different manner: --------------- ---------------- ------------------- | car | cdr | | car | cdr | | car | cdr | | rose | o-------->| violet | o-------->| buttercup | nil | | | | | | | | | | --------------- ---------------- ------------------- A list with no elements in it is the "empty list"; it is identical to the symbol `nil'. In other words, `nil' is both a symbol and a list. Here are examples of lists written in Lisp syntax: (A 2 "A") ; A list of three elements. () ; A list of no elements (the empty list). nil ; A list of no elements (the empty list). ("A ()") ; A list of one element: the string `"A ()"'. (A ()) ; A list of two elements: `A' and the empty list. (A nil) ; Equivalent to the previous. ((A B C)) ; A list of one element ; (which is a list of three elements). Here is the list `(A ())', or equivalently `(A nil)', depicted with boxes and arrows: ___ ___ ___ ___ |___|___|--> |___|___|--> nil | | | | --> A --> nil * Menu: * Dotted Pair Notation:: An alternative syntax for lists. * Association List Type:: A specially constructed list. File: lispref.info, Node: Dotted Pair Notation, Next: Association List Type, Up: Cons Cell Type Dotted Pair Notation .................... "Dotted pair notation" is an alternative syntax for cons cells that represents the CAR and CDR explicitly. In this syntax, `(A . B)' stands for a cons cell whose CAR is the object A, and whose CDR is the object B. Dotted pair notation is therefore more general than list syntax. In the dotted pair notation, the list `(1 2 3)' is written as `(1 . (2 . (3 . nil)))'. For `nil'-terminated lists, the two notations produce the same result, but list notation is usually clearer and more convenient when it is applicable. When printing a list, the dotted pair notation is only used if the CDR of a cell is not a list. Here's how box notation can illustrate dotted pairs. This example shows the pair `(rose . violet)': ___ ___ |___|___|--> violet | | --> rose Dotted pair notation can be combined with list notation to represent a chain of cons cells with a non-`nil' final CDR. For example, `(rose violet . buttercup)' is equivalent to `(rose . (violet . buttercup))'. The object looks like this: ___ ___ ___ ___ |___|___|--> |___|___|--> buttercup | | | | --> rose --> violet These diagrams make it evident why `(rose . violet . buttercup)' is invalid syntax; it would require a cons cell that has three parts rather than two. The list `(rose violet)' is equivalent to `(rose . (violet))' and looks like this: ___ ___ ___ ___ |___|___|--> |___|___|--> nil | | | | --> rose --> violet Similarly, the three-element list `(rose violet buttercup)' is equivalent to `(rose . (violet . (buttercup)))'. It looks like this: ___ ___ ___ ___ ___ ___ |___|___|--> |___|___|--> |___|___|--> nil | | | | | | --> rose --> violet --> buttercup File: lispref.info, Node: Association List Type, Prev: Dotted Pair Notation, Up: Cons Cell Type Association List Type ..................... An "association list" or "alist" is a specially-constructed list whose elements are cons cells. In each element, the CAR is considered a "key", and the CDR is considered an "associated value". (In some cases, the associated value is stored in the CAR of the CDR.) Association lists are often used as stacks, since it is easy to add or remove associations at the front of the list. For example, (setq alist-of-colors '((rose . red) (lily . white) (buttercup . yellow))) sets the variable `alist-of-colors' to an alist of three elements. In the first element, `rose' is the key and `red' is the value. *Note Association Lists::, for a further explanation of alists and for functions that work on alists. File: lispref.info, Node: Array Type, Next: String Type, Prev: Cons Cell Type, Up: Programming Types Array Type ---------- An "array" is composed of an arbitrary number of slots for referring to other Lisp objects, arranged in a contiguous block of memory. Accessing any element of an array takes the same amount of time. In contrast, accessing an element of a list requires time proportional to the position of the element in the list. (Elements at the end of a list take longer to access than elements at the beginning of a list.) XEmacs defines three types of array, strings, vectors, and bit vectors. A string is an array of characters, a vector is an array of arbitrary objects, and a bit vector is an array of 1's and 0's. All are one-dimensional. (Most other programming languages support multidimensional arrays, but they are not essential; you can get the same effect with an array of arrays.) Each type of array has its own read syntax; see *Note String Type::, *Note Vector Type::, and *Note Bit Vector Type::. An array may have any length up to the largest integer; but once created, it has a fixed size. The first element of an array has index zero, the second element has index 1, and so on. This is called "zero-origin" indexing. For example, an array of four elements has indices 0, 1, 2, and 3. The array type is contained in the sequence type and contains the string type, the vector type, and the bit vector type. File: lispref.info, Node: String Type, Next: Vector Type, Prev: Array Type, Up: Programming Types String Type ----------- A "string" is an array of characters. Strings are used for many purposes in XEmacs, as can be expected in a text editor; for example, as the names of Lisp symbols, as messages for the user, and to represent text extracted from buffers. Strings in Lisp are constants: evaluation of a string returns the same string. The read syntax for strings is a double-quote, an arbitrary number of characters, and another double-quote, `"like this"'. The Lisp reader accepts the same formats for reading the characters of a string as it does for reading single characters (without the question mark that begins a character literal). You can enter a nonprinting character such as tab or `C-a' using the convenient escape sequences, like this: `"\t, \C-a"'. You can include a double-quote in a string by preceding it with a backslash; thus, `"\""' is a string containing just a single double-quote character. (*Note Character Type::, for a description of the read syntax for characters.) The printed representation of a string consists of a double-quote, the characters it contains, and another double-quote. However, you must escape any backslash or double-quote characters in the string with a backslash, like this: `"this \" is an embedded quote"'. The newline character is not special in the read syntax for strings; if you write a new line between the double-quotes, it becomes a character in the string. But an escaped newline--one that is preceded by `\'--does not become part of the string; i.e., the Lisp reader ignores an escaped newline while reading a string. "It is useful to include newlines in documentation strings, but the newline is \ ignored if escaped." => "It is useful to include newlines in documentation strings, but the newline is ignored if escaped." A string can hold extents and properties of the text it contains, in addition to the characters themselves. This enables programs that copy text between strings and buffers to preserve the extents and properties with no special effort. *Note Extents::; *Note Text Properties::. Note that FSF GNU Emacs has a special read and print syntax for strings with text properties, but XEmacs does not currently implement this. It was judged better not to include this in XEmacs because it entails that `equal' return `nil' when passed a string with text properties and the equivalent string without text properties, which is often counter-intuitive. *Note Strings and Characters::, for functions that work on strings. File: lispref.info, Node: Vector Type, Next: Bit Vector Type, Prev: String Type, Up: Programming Types Vector Type ----------- A "vector" is a one-dimensional array of elements of any type. It takes a constant amount of time to access any element of a vector. (In a list, the access time of an element is proportional to the distance of the element from the beginning of the list.) The printed representation of a vector consists of a left square bracket, the elements, and a right square bracket. This is also the read syntax. Like numbers and strings, vectors are considered constants for evaluation. [1 "two" (three)] ; A vector of three elements. => [1 "two" (three)] *Note Vectors::, for functions that work with vectors. File: lispref.info, Node: Bit Vector Type, Next: Function Type, Prev: Vector Type, Up: Programming Types Bit Vector Type --------------- A "bit vector" is a one-dimensional array of 1's and 0's. It takes a constant amount of time to access any element of a bit vector, as for vectors. Bit vectors have an extremely compact internal representation (one machine bit per element), which makes them ideal for keeping track of unordered sets, large collections of boolean values, etc. The printed representation of a bit vector consists of `#*' followed by the bits in the vector. This is also the read syntax. Like numbers, strings, and vectors, bit vectors are considered constants for evaluation. #*00101000 ; A bit vector of eight elements. => #*00101000 *Note Bit Vectors::, for functions that work with bit vectors. File: lispref.info, Node: Function Type, Next: Macro Type, Prev: Bit Vector Type, Up: Programming Types Function Type ------------- Just as functions in other programming languages are executable, "Lisp function" objects are pieces of executable code. However, functions in Lisp are primarily Lisp objects, and only secondarily the text which represents them. These Lisp objects are lambda expressions: lists whose first element is the symbol `lambda' (*note Lambda Expressions::.). In most programming languages, it is impossible to have a function without a name. In Lisp, a function has no intrinsic name. A lambda expression is also called an "anonymous function" (*note Anonymous Functions::.). A named function in Lisp is actually a symbol with a valid function in its function cell (*note Defining Functions::.). Most of the time, functions are called when their names are written in Lisp expressions in Lisp programs. However, you can construct or obtain a function object at run time and then call it with the primitive functions `funcall' and `apply'. *Note Calling Functions::. File: lispref.info, Node: Macro Type, Next: Primitive Function Type, Prev: Function Type, Up: Programming Types Macro Type ---------- A "Lisp macro" is a user-defined construct that extends the Lisp language. It is represented as an object much like a function, but with different parameter-passing semantics. A Lisp macro has the form of a list whose first element is the symbol `macro' and whose CDR is a Lisp function object, including the `lambda' symbol. Lisp macro objects are usually defined with the built-in `defmacro' function, but any list that begins with `macro' is a macro as far as XEmacs is concerned. *Note Macros::, for an explanation of how to write a macro. File: lispref.info, Node: Primitive Function Type, Next: Compiled-Function Type, Prev: Macro Type, Up: Programming Types Primitive Function Type ----------------------- A "primitive function" is a function callable from Lisp but written in the C programming language. Primitive functions are also called "subrs" or "built-in functions". (The word "subr" is derived from "subroutine".) Most primitive functions evaluate all their arguments when they are called. A primitive function that does not evaluate all its arguments is called a "special form" (*note Special Forms::.). It does not matter to the caller of a function whether the function is primitive. However, this does matter if you try to substitute a function written in Lisp for a primitive of the same name. The reason is that the primitive function may be called directly from C code. Calls to the redefined function from Lisp will use the new definition, but calls from C code may still use the built-in definition. The term "function" refers to all Emacs functions, whether written in Lisp or C. *Note Function Type::, for information about the functions written in Lisp. Primitive functions have no read syntax and print in hash notation with the name of the subroutine. (symbol-function 'car) ; Access the function cell ; of the symbol. => #<subr car> (subrp (symbol-function 'car)) ; Is this a primitive function? => t ; Yes. File: lispref.info, Node: Compiled-Function Type, Next: Autoload Type, Prev: Primitive Function Type, Up: Programming Types Compiled-Function Type ---------------------- The byte compiler produces "compiled-function objects". The evaluator handles this data type specially when it appears as a function to be called. *Note Byte Compilation::, for information about the byte compiler. The printed representation for a compiled-function object is normally `#<compiled-function...>'. If `print-readably' is true, however, it is `#[...]'. File: lispref.info, Node: Autoload Type, Next: Char Table Type, Prev: Compiled-Function Type, Up: Programming Types Autoload Type ------------- An "autoload object" is a list whose first element is the symbol `autoload'. It is stored as the function definition of a symbol as a placeholder for the real definition; it says that the real definition is found in a file of Lisp code that should be loaded when necessary. The autoload object contains the name of the file, plus some other information about the real definition. After the file has been loaded, the symbol should have a new function definition that is not an autoload object. The new definition is then called as if it had been there to begin with. From the user's point of view, the function call works as expected, using the function definition in the loaded file. An autoload object is usually created with the function `autoload', which stores the object in the function cell of a symbol. *Note Autoload::, for more details. File: lispref.info, Node: Char Table Type, Next: Hash Table Type, Prev: Autoload Type, Up: Programming Types Char Table Type --------------- (not yet documented) File: lispref.info, Node: Hash Table Type, Next: Range Table Type, Prev: Char Table Type, Up: Programming Types Hash Table Type --------------- A "hash table" is a table providing an arbitrary mapping from one Lisp object to another, using an internal indexing method called "hashing". Hash tables are very fast (much more efficient that using an association list, when there are a large number of elements in the table). Hash tables have no read syntax. They print in hash notation (The "hash" in "hash notation" has nothing to do with the "hash" in "hash table"), giving the number of elements, total space allocated for elements, and a unique number assigned at the time the hash table was created. (Hash tables automatically resize as necessary so there is no danger of running out of space for elements.) (make-hashtable 50) => #<hashtable 0/71 0x313a> *Note Hash Tables::, for information on how to create and work with hash tables. File: lispref.info, Node: Range Table Type, Next: Weak List Type, Prev: Hash Table Type, Up: Programming Types Range Table Type ---------------- A "range table" is a table that maps from ranges of integers to arbitrary Lisp objects. Range tables automatically combine overlapping ranges that map to the same Lisp object, and operations are provided for mapping over all of the ranges in a range table. Range tables have a special read syntax beginning with `#s(range-table' (this is an example of "structure" read syntax, which is also used for char tables and faces). (setq x (make-range-table)) (put-range-table 20 50 'foo x) (put-range-table 100 200 "bar" x) x => #s(range-table data ((20 50) foo (100 200) "bar")) *Note Range Tables::, for information on how to create and work with range tables. File: lispref.info, Node: Weak List Type, Prev: Range Table Type, Up: Programming Types Weak List Type -------------- (not yet documented) File: lispref.info, Node: Editing Types, Next: Window-System Types, Prev: Programming Types, Up: Lisp Data Types Editing Types ============= The types in the previous section are common to many Lisp dialects. XEmacs Lisp provides several additional data types for purposes connected with editing. * Menu: * Buffer Type:: The basic object of editing. * Marker Type:: A position in a buffer. * Extent Type:: A range in a buffer or string, maybe with properties. * Window Type:: Buffers are displayed in windows. * Frame Type:: Windows subdivide frames. * Device Type:: Devices group all frames on a display. * Console Type:: Consoles group all devices with the same keyboard. * Window Configuration Type:: Recording the way a frame is subdivided. * Event Type:: An interesting occurrence in the system. * Process Type:: A process running on the underlying OS. * Stream Type:: Receive or send characters. * Keymap Type:: What function a keystroke invokes. * Syntax Table Type:: What a character means. * Display Table Type:: How display tables are represented. * Database Type:: A connection to an external DBM or DB database. * Charset Type:: A character set (e.g. all Kanji characters), under XEmacs/MULE. * Coding System Type:: An object encapsulating a way of converting between different textual encodings, under XEmacs/MULE. * ToolTalk Message Type:: A message, in the ToolTalk IPC protocol. * ToolTalk Pattern Type:: A pattern, in the ToolTalk IPC protocol. File: lispref.info, Node: Buffer Type, Next: Marker Type, Up: Editing Types Buffer Type ----------- A "buffer" is an object that holds text that can be edited (*note Buffers::.). Most buffers hold the contents of a disk file (*note Files::.) so they can be edited, but some are used for other purposes. Most buffers are also meant to be seen by the user, and therefore displayed, at some time, in a window (*note Windows::.). But a buffer need not be displayed in any window. The contents of a buffer are much like a string, but buffers are not used like strings in XEmacs Lisp, and the available operations are different. For example, insertion of text into a buffer is very efficient, whereas "inserting" text into a string requires concatenating substrings, and the result is an entirely new string object. Each buffer has a designated position called "point" (*note Positions::.). At any time, one buffer is the "current buffer". Most editing commands act on the contents of the current buffer in the neighborhood of point. Many of the standard Emacs functions manipulate or test the characters in the current buffer; a whole chapter in this manual is devoted to describing these functions (*note Text::.). Several other data structures are associated with each buffer: * a local syntax table (*note Syntax Tables::.); * a local keymap (*note Keymaps::.); * a local variable binding list (*note Buffer-Local Variables::.); * a list of extents (*note Extents::.); * and various other related properties. The local keymap and variable list contain entries that individually override global bindings or values. These are used to customize the behavior of programs in different buffers, without actually changing the programs. A buffer may be "indirect", which means it shares the text of another buffer. *Note Indirect Buffers::. Buffers have no read syntax. They print in hash notation, showing the buffer name. (current-buffer) => #<buffer "objects.texi"> File: lispref.info, Node: Marker Type, Next: Extent Type, Prev: Buffer Type, Up: Editing Types Marker Type ----------- A "marker" denotes a position in a specific buffer. Markers therefore have two components: one for the buffer, and one for the position. Changes in the buffer's text automatically relocate the position value as necessary to ensure that the marker always points between the same two characters in the buffer. Markers have no read syntax. They print in hash notation, giving the current character position and the name of the buffer. (point-marker) => #<marker at 50661 in objects.texi> *Note Markers::, for information on how to test, create, copy, and move markers. File: lispref.info, Node: Extent Type, Next: Window Type, Prev: Marker Type, Up: Editing Types Extent Type ----------- An "extent" specifies temporary alteration of the display appearance of a part of a buffer (or string). It contains markers delimiting a range of the buffer, plus a property list (a list whose elements are alternating property names and values). Extents are used to present parts of the buffer temporarily in a different display style. They have no read syntax, and print in hash notation, giving the buffer name and range of positions. Extents can exist over strings as well as buffers; the primary use of this is to preserve extent and text property information as text is copied from one buffer to another or between different parts of a buffer. Extents have no read syntax. They print in hash notation, giving the range of text they cover, the name of the buffer or string they are in, the address in core, and a summary of some of the properties attached to the extent. (extent-at (point)) => #<extent [51742, 51748) font-lock text-prop 0x90121e0 in buffer objects.texi> *Note Extents::, for how to create and use extents. Extents are used to implement text properties. *Note Text Properties::. File: lispref.info, Node: Window Type, Next: Frame Type, Prev: Extent Type, Up: Editing Types Window Type ----------- A "window" describes the portion of the frame that XEmacs uses to display a buffer. (In standard window-system usage, a "window" is what XEmacs calls a "frame"; XEmacs confusingly uses the term "window" to refer to what is called a "pane" in standard window-system usage.) Every window has one associated buffer, whose contents appear in the window. By contrast, a given buffer may appear in one window, no window, or several windows. Though many windows may exist simultaneously, at any time one window is designated the "selected window". This is the window where the cursor is (usually) displayed when XEmacs is ready for a command. The selected window usually displays the current buffer, but this is not necessarily the case. Windows are grouped on the screen into frames; each window belongs to one and only one frame. *Note Frame Type::. Windows have no read syntax. They print in hash notation, giving the name of the buffer being displayed and a unique number assigned at the time the window was created. (This number can be useful because the buffer displayed in any given window can change frequently.) (selected-window) => #<window on "objects.texi" 0x266c> *Note Windows::, for a description of the functions that work on windows. File: lispref.info, Node: Frame Type, Next: Device Type, Prev: Window Type, Up: Editing Types Frame Type ---------- A FRAME is a rectangle on the screen (a "window" in standard window-system terminology) that contains one or more non-overlapping Emacs windows ("panes" in standard window-system terminology). A frame initially contains a single main window (plus perhaps a minibuffer window) which you can subdivide vertically or horizontally into smaller windows. Frames have no read syntax. They print in hash notation, giving the frame's type, name as used for resourcing, and a unique number assigned at the time the frame was created. (selected-frame) => #<x-frame "emacs" 0x9db> *Note Frames::, for a description of the functions that work on frames. File: lispref.info, Node: Device Type, Next: Console Type, Prev: Frame Type, Up: Editing Types Device Type ----------- A "device" represents a single display on which frames exist. Normally, there is only one device object, but there may be more than one if XEmacs is being run on a multi-headed display (e.g. an X server with attached color and mono screens) or if XEmacs is simultaneously driving frames attached to different consoles, e.g. an X display and a TTY connection. Devices do not have a read syntax. They print in hash notation, giving the device's type, connection name, and a unique number assigned at the time the device was created. (selected-device) => #<x-device on ":0.0" 0x5b9> *Note Consoles and Devices::, for a description of several functions related to devices. File: lispref.info, Node: Console Type, Next: Window Configuration Type, Prev: Device Type, Up: Editing Types Console Type ------------ A "console" represents a single keyboard to which devices (i.e. displays on which frames exist) are connected. Normally, there is only one console object, but there may be more than one if XEmacs is simultaneously driving frames attached to different X servers and/or TTY connections. (XEmacs is capable of driving multiple X and TTY connections at the same time, and provides a robust mechanism for handling the differing display capabilities of such heterogeneous environments. A buffer with embedded glyphs and multiple fonts and colors, for example, will display reasonably if it simultaneously appears on a frame on a color X display, a frame on a mono X display, and a frame on a TTY connection.) Consoles do not have a read syntax. They print in hash notation, giving the console's type, connection name, and a unique number assigned at the time the console was created. (selected-console) => #<x-console on "localhost:0" 0x5b7> *Note Consoles and Devices::, for a description of several functions related to consoles. File: lispref.info, Node: Window Configuration Type, Next: Event Type, Prev: Console Type, Up: Editing Types Window Configuration Type ------------------------- A "window configuration" stores information about the positions, sizes, and contents of the windows in a frame, so you can recreate the same arrangement of windows later. Window configurations do not have a read syntax. They print in hash notation, giving a unique number assigned at the time the window configuration was created. (current-window-configuration) => #<window-configuration 0x2db4> *Note Window Configurations::, for a description of several functions related to window configurations. File: lispref.info, Node: Event Type, Next: Process Type, Prev: Window Configuration Type, Up: Editing Types Event Type ---------- (not yet documented) File: lispref.info, Node: Process Type, Next: Stream Type, Prev: Event Type, Up: Editing Types Process Type ------------ The word "process" usually means a running program. XEmacs itself runs in a process of this sort. However, in XEmacs Lisp, a process is a Lisp object that designates a subprocess created by the XEmacs process. Programs such as shells, GDB, ftp, and compilers, running in subprocesses of XEmacs, extend the capabilities of XEmacs. An Emacs subprocess takes textual input from Emacs and returns textual output to Emacs for further manipulation. Emacs can also send signals to the subprocess. Process objects have no read syntax. They print in hash notation, giving the name of the process, its associated process ID, and the current state of the process: (process-list) => (#<process "shell" pid 2909 state:run>) *Note Processes::, for information about functions that create, delete, return information about, send input or signals to, and receive output from processes. File: lispref.info, Node: Stream Type, Next: Keymap Type, Prev: Process Type, Up: Editing Types Stream Type ----------- A "stream" is an object that can be used as a source or sink for characters--either to supply characters for input or to accept them as output. Many different types can be used this way: markers, buffers, strings, and functions. Most often, input streams (character sources) obtain characters from the keyboard, a buffer, or a file, and output streams (character sinks) send characters to a buffer, such as a `*Help*' buffer, or to the echo area. The object `nil', in addition to its other meanings, may be used as a stream. It stands for the value of the variable `standard-input' or `standard-output'. Also, the object `t' as a stream specifies input using the minibuffer (*note Minibuffers::.) or output in the echo area (*note The Echo Area::.). Streams have no special printed representation or read syntax, and print as whatever primitive type they are. *Note Read and Print::, for a description of functions related to streams, including parsing and printing functions. File: lispref.info, Node: Keymap Type, Next: Syntax Table Type, Prev: Stream Type, Up: Editing Types Keymap Type ----------- A "keymap" maps keys typed by the user to commands. This mapping controls how the user's command input is executed. NOTE: In XEmacs, a keymap is a separate primitive type. In FSF GNU Emacs, a keymap is actually a list whose CAR is the symbol `keymap'. *Note Keymaps::, for information about creating keymaps, handling prefix keys, local as well as global keymaps, and changing key bindings. File: lispref.info, Node: Syntax Table Type, Next: Display Table Type, Prev: Keymap Type, Up: Editing Types Syntax Table Type ----------------- Under XEmacs 20, a "syntax table" is a particular type of char table. Under XEmacs 19, a syntax table a vector of 256 integers. In both cases, each element defines how one character is interpreted when it appears in a buffer. For example, in C mode (*note Major Modes::.), the `+' character is punctuation, but in Lisp mode it is a valid character in a symbol. These modes specify different interpretations by changing the syntax table entry for `+'. Syntax tables are used only for scanning text in buffers, not for reading Lisp expressions. The table the Lisp interpreter uses to read expressions is built into the XEmacs source code and cannot be changed; thus, to change the list delimiters to be `{' and `}' instead of `(' and `)' would be impossible. *Note Syntax Tables::, for details about syntax classes and how to make and modify syntax tables. File: lispref.info, Node: Display Table Type, Next: Database Type, Prev: Syntax Table Type, Up: Editing Types Display Table Type ------------------ A "display table" specifies how to display each character code. Each buffer and each window can have its own display table. A display table is actually a vector of length 256, although in XEmacs 20 this may change to be a particular type of char table. *Note Display Tables::. File: lispref.info, Node: Database Type, Next: Charset Type, Prev: Display Table Type, Up: Editing Types Database Type ------------- (not yet documented) File: lispref.info, Node: Charset Type, Next: Coding System Type, Prev: Database Type, Up: Editing Types Charset Type ------------ (not yet documented) File: lispref.info, Node: Coding System Type, Next: ToolTalk Message Type, Prev: Charset Type, Up: Editing Types Coding System Type ------------------ (not yet documented) File: lispref.info, Node: ToolTalk Message Type, Next: ToolTalk Pattern Type, Prev: Coding System Type, Up: Editing Types ToolTalk Message Type --------------------- (not yet documented) File: lispref.info, Node: ToolTalk Pattern Type, Prev: ToolTalk Message Type, Up: Editing Types ToolTalk Pattern Type --------------------- (not yet documented) File: lispref.info, Node: Window-System Types, Next: Type Predicates, Prev: Editing Types, Up: Lisp Data Types Window-System Types =================== XEmacs also has some types that represent objects such as faces (collections of display characters), fonts, and pixmaps that are commonly found in windowing systems. * Menu: * Face Type:: A collection of display characteristics. * Glyph Type:: An image appearing in a buffer or elsewhere. * Specifier Type:: A way of controlling display characteristics on a per-buffer, -frame, -window, or -device level. * Font Instance Type:: The way a font appears on a particular device. * Color Instance Type:: The way a color appears on a particular device. * Image Instance Type:: The way an image appears on a particular device. * Toolbar Button Type:: An object representing a button in a toolbar. * Subwindow Type:: An externally-controlled window-system window appearing in a buffer. * X Resource Type:: A miscellaneous X resource, if Epoch support was compiled into XEmacs. File: lispref.info, Node: Face Type, Next: Glyph Type, Up: Window-System Types Face Type --------- (not yet documented) File: lispref.info, Node: Glyph Type, Next: Specifier Type, Prev: Face Type, Up: Window-System Types Glyph Type ---------- (not yet documented) File: lispref.info, Node: Specifier Type, Next: Font Instance Type, Prev: Glyph Type, Up: Window-System Types Specifier Type -------------- (not yet documented)